MathDB
Sequence appears to grow quite quickly. Is it always positive?

Source: 2019 Pan-African Shortlist - A5

January 18, 2021
algebraSequencesnumber base

Problem Statement

Let a sequence (ai)i=10(a_i)_{i=10}^{\infty} be defined as follows:
[*] a10a_{10} is some positive integer, which can of course be written in base 10. [*] For i10i \geq 10 if ai>0a_i > 0, let bib_i be the positive integer whose base-(i+1)(i + 1) representation is the same as aia_i's base-ii representation. Then let ai+1=bi1a_{i + 1} = b_i - 1. If ai=0a_i = 0, ai+1=0a_{i + 1} = 0.
For example, if a10=11a_{10} = 11, then b10=1111(=1210)b_{10} = 11_{11} (= 12_{10}); a11=11111=1011(=1110)a_{11} = 11_{11} - 1 = 10_{11} (= 11_{10}); b11=1012(=1210)b_{11} = 10_{12} (= 12_{10}); a12=11a_{12} = 11.
Does there exist a10a_{10} such that aia_i is strictly positive for all i10i \geq 10?